King Yao: author of Weighing the Odds in Sports Betting and Weighing the Odds in Hold'em Poker

Thursday, September 06, 2007

NFL Interceptions prop bets

I found some year-long prop bets in the NFL that I think have edge. The props were on the total interceptions made by each team's defense. I bet the Under on 17 different teams (listed below). The limits are low, but they add up over 17 different bets that represent the same idea.

Taking the shotgun approach, I bet the under on any total of 16.5 or higher. Here's my rationale:

Over the last 4 years (2002-2006), the average number of INTs made was 15.85, with the median at 15.

For the 32 teams over the last 4 seasons (128 total teams), if the total was 16.5, the Under won 77 times and lost 51. For a winning percentage of 60.2% or about -150.

The initial question is: "So what? You need to take into account the good defenses as they are likely to have higher INT totals."

And I did that. I took teams with 18 or more INTs and compared how they did in the next year versus a total of less than 3.5 INTs, but with a minimum of 16.5. For example, if BAL had 20 INTs in 2003, then I would look how BAL did versus a total of 16.5 in 2004.

The total record against a total of 3.5 fewer INTs the following year, but no lower than 16.5, was 7-20.

Next, I ran correlation numbers. Using 2003-2005 INT numbers and correlating it to 2004-2006 INT numbers for the same teams. The correlation was a paltry 0.02. This along may be enough reason to bet Under on high totals.

To top it off, the 17 teams that I bet, which all had totals of 16.5 or greater, had an average number of INTs fewer last year than the total. The average line I bet into was 18.5. The teams that I wagered Under on averaged 17.6 interceptions last year.